Stripline and other transmission line type filters have been used in miniature electronic devices to provide filters of small size which can be constructed at low cost. In such filters, the frequency response depends upon the configuration of the conducting layer which forms the edge coupled transmission lines, and the dielectric constant of the surrounding material. When such a filter is provided by production techniques used for low cost construction, variations in the dielectric constant of the material and in the dimensions will occur, which may result in substantial changes in the frequency response, so that the resulting filters may have a frequency response outside the desired frequency limits.
It has been proposed to use adjustable devices, such as trimming screws or external capacitors, with stripline filters to change the response frequency of the filter. Also, clamping arrangements have been used to compress the dielectric material and thereby change the electrical parameters of the line. However, these devices have substantially increased the size and cost of the filter so that this has not been a satisfactory solution.